Future work

In this report，we discovered that the epitaxial layer grown on patterned sapphire substrate was provided with better quality. Besides, PSS structure can redirect the light emitted from active layer toward to the exit cone of the LED surface as well as enhance extraction efficiency.

In the future, we will try to fabricate double-side patterned substrate. Using photolithography and H3PO4-based solution at an etching temperature of 300 ^oC etch the back side of PSS. Al metal with a reflectivity of about 90 % was then deposited on that surface.

Subsequently, we will grow epitaxial layer and carry out othe processes. Furthermore, we will try to combine two structures, V-shape sapphire facet reflector LED and CWE-PSS LED, with other structures, for instance, p-GaN surface roughening process or photonic crystal(Fig.

5-1).

Fig. 5-1 double-side patterned sapphire substrate LED

Reference

[1] S. Nakamura, G. Fasol, “The Blue Laser Diode,” Springer, New York, 1997.

[2] S. Nakamura, M. Senoh, N. Iwasa, and S. Nagahama, “High-brightness InGaN blue, green and yellow light-emitting diodes with quantum well structures,” Jpn. J. Appl. Phys., vol. 34, p.

L797, 1995.

[3] H. Morkoc, S. Strite, G.B. Gao, M.E. Lin, B. Sverdlov, M. Burns, “Large-band-gap SIC, III-V nitride, and II-VI ZnSe-based semiconductor device technologies,” J. Appl. Phys. vol.76, pp1363–1398, 1994.

[4] M. Koike, N. Shibata, H. Kato, and Y. Takahashi, “Development of High Efficiency GaN-Based Multiquantum-Well Light-Emitting Diodes and Their Applications,” IEEE JOURNAL ON SELECTED TOPICS IN QUANTUM ELECTRONICS, vol. 8, pp 271-277, 2002.

[5] S. H. Lydecker, K. F. Leadford, C. A. Ooyen, “Lighting Industry Acceptance of Solid State Lighting,” Proc. of SPIE, vol. 5187, pp 22-33, 2004.

[6] Jianghong Jiao, Ben Wang, “Etendue Concerns for Automotive Headlamps Using White LEDs, Proc. of SPIE, vol. 5187, pp 234-242, 2004.

[7] S.D. Lester, F.A. Ponce, M.G. Craford and D.A.Steigerwald, “High dislocation densities in high efficiency GaN-based light-emitting diodes ”, Appl. Phys. Lett. vol.66, pp1249-1251, 1995.

[8] M. Broditsky and E. Yablonovitch, “Light-emitting-diode extraction efficiency,” Proc.

Spie, vol. 3002, pp119-122, 1997.

[9] M.R. Krames, M. Ochiai-Holcomb, G. E. Höfler, C. Carter-Coman, E. I. Chen, I. –H. Tan, P. Grillot, N. F. Gardner, H. F. Gardner, H.C. Chui, J. -W. Huang, S. A. Stockman, F. A. Kish, and M. G. Craford, “High-power truncated-inverted-pyramid (AlxGa1–x)0.5In0.5P/GaP light-emitting diodes exhibiting >50 external quantum efficiency,” Appl. Phys. Lett. vol. 75, pp2365-2367, 1999.

[10] C. Huh, K.-S. Lee, E.-J. Kang, and S.-J. Park, “Improved light-outputand electrical performance of InGaN-based light-emitting diode by microroughening of the p-GaN surface,”

J. Appl. Phys., vol. 93, pp.9383–9383, 2003.

[11] S. J. Chang, L. W. Wu, Y. K. Su, Y. P. Hsu, W. C. Lai, J. M. Tsai, J. K. Sheu, and C. T.

Lee, “Nitride-based LEDs with 800 C grown p-AlInGaN-GaN double-cap layers,” IEEE Photon. Technol. Lett., vol.16, no. 6, pp. 1447–1449, Jun. 2004.

[12] Y. Gao, T. Fujii, R. Sharma, K. Fujito, S. P. Denbaars, S. Nakamura, and

E. L. Hu, “Roughening hexagonal surface morphology on laser lift-off (LLO) N-face GaN with simple photo-enhanced chemical wet etching,” Jpn. J. Appl. Phys., vol. 43, pp. 637–637, 2004.

[13] T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the

extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys.

Lett., vol. 84, pp. 855–855, 2004.

[14] T. N. Oder, K. H. Kim, J. Y. Lin, and H. X. Jiang, “III-nitride blue and ultraviolet photonic crystal light emitting diodes,” Appl. Phys. Lett., vol. 84, pp. 466–468, 2004.

[15] C. C. Kao, H. C. Kuo, H. W. Huang, J. T. Chu, Y. C. Peng, Y. L. Hsieh, C. Y. Luo, and S.

C. Wang, “Light-output enhancement in a nitride-based light-emitting diode with 22^o undercut sidewalls,” IEEE Photon. Technol. Lett. vol. 17, pp 19-21, 2005.

[16] H. W. Huang, C. C. Kao, J. T. Chu, H. C. Kuo, S. C. Wang, and C. C. Yu, “Improvement of InGaN–GaN Light-Emitting Diode Performance With a Nano-Roughened p-GaN Surface,”

IEEE Photon. Technol. Lett. vol. 17, pp 983-985, 2005.

[17] Y. J. Lee, H. C. Kuo, S. C. Wang, T. C. Hsu, M. H. Hsieh, M. J. Jou, and B. J. Lee

“Increasing the extraction efficiency of AlGaInP LEDs via n-side surface roughening ”, IEEE Photonic Technology Letter, vol. 17, pp2289-2291, 2005.

[18] Y. J. Lee, H. C. Tseng, H. C. Kuo, S. C. Wang, C. W. Chang, T. C. Hsu, Y. L. Yang, M.

H. Hsieh, M. J. Jou, and B. J. Lee, “Improvement in Light-Output Efficiency of AlGaInP LEDs Fabricated on Stripe Patterned Epitaxy”, IEEE Photonic Technology Letter, vol. 17, pp2532-2534, 2005.

[19] Y. J. Lee, T.C. Lu, H.C. Kuo, S.C. Wang, M. J. Liou, C.W. Chang, T. C. Hsu, M. H.

Hsieh, M. J. Jou, and B. J. Lee, “AlGaInP LEDs with Stripe Patterned Omni-Directional Reflector”, Jpn. J. Appl. Phys., vol. 45, pp643-645, 2006.

[20] Y. J. Lee, T.C. Lu, H.C. Kuo, S.C. Wang, M. J. Liou, C.W. Chang, T. C. Hsu, M. H.

Hsieh, M. J. Jou, and B. J. Lee, “High brightness AlGaInP-based light emitting diodes by adopting the stripe-patterned omni-directional reflector”, Semicond. Sci. Technol. vol.21, pp.184–189, 2006.

[21] Y. J. Lee, J.M. Hwang, T. C. Hsu, M. H. Hsieh, M. J. Jou, B. J. Lee, T.C. Lu, H.C.Kuo, and S.C. Wang, “GaN-based LEDs with Al-Deposited V-Shape Sapphire Facet Mirror,” IEEE Photon. Technol. Lett, accepted for publication, vol.18, 2006.

[22] K. Tadatomo, H. Okagawa, Y. Ohuchi, T. Tsunekawa, Y. Imada, M. Kato, T. Taguchi,

“ High Output Power InGaN Ultraviolet Light Emitting Diodes Fabricated on Patterned Substrates Using Metalorganic Vapor Phase Epitaxy,” Jpn. J. Appl. Phys. vol. 40, L583–L585, 2001.

[23] M. Yamada, T. Mitani, Y. Narukawa, S. Shioji, I. Niki, S. Sonobe, K. Deguchi, M. Sano, T. Mukai, “InGaN-Based Near-Ultraviolet and Blue-Light-Emitting Diodes with High External Quantum Efficiency Using a Patterned Sapphire Substrate and a Mesh Electrode,”

Jpn. J. Appl. Phys. vol. 41, L1431–L1433, 2002.

[24] D.S. Wuu, W.K. Wang, W.C. Shih, R.H. Horng, C.E. Lee, W.Y. Lin, J.S. Fang,

“Enhanced Output Power of Near-Ultraviolet InGaN–GaN LEDs Grown on Patterned Sapphire Substrates,” IEEE Photon. Technol. Lett. vol.17, pp. 288– 290, 2005

[25] Z. H. Feng, and Kei May Lau, “Enhanced Luminescence From GaN-Based Blue

LEDs Grown on Grooved Sapphire Substrates,” IEEE Photon. Technol. Lett. vol.17, pp.

1812– 1814, 2005.

[26] Y. J. Lee, T. C. Hsu, H.C. Kuo, S.C. Wang, Y.L. Yang, S.N. Yen, Y.T. Chu, Y.J. Shen, M.H. Hsieh, M.J. Jou, B.J. Lee, “Improvement in light-output efficiency of Near-Ultraviolet InGaN–GaN LEDs Fabricated on Stripe Patterned Sapphire Substrates”, Material Science and Engineering: B, vol. 122, pp184-187, 2005.

[27] Y. J. Lee, J.M.Hwang, T. C. Hsu, M. H. Hsieh, M. J. Jou, B. J. Lee, T.C. Lu, H.C. Kuo, and S.C. Wang, “Enhancing Output Power of GaN-based LEDs Grown on Chemical Wet Etching Patterned Sapphire Substrate,” revised for publication, IEEE Photonic Technology Letter, 2006.

[28] J. Wang, L. W. Guo, H. Q. Jia, Z. G. Xing, Y. Wang, H. Chen and J. M. Zhou, “ Origin of Selective Growth of GaN on Maskless V-Grooved Sapphire Substrate by Metalorganic Chemical Vapor Deposition,” Jpn. J. Appl. Phys., vol. 44, pp. L982-L984, 2005